In typical papermaking processes, a general correlation exists between fiber coarseness and softness or handfeel of the resulting paper product.
Expensive high quality fibers such as bleached northern softwood kraft fibers are fine, flexible and are used to produce soft, desirable tissue products. In contrast, mechanical pulping of softwoods produces high-yield, coarse, stiff fibers typically used to make newsprint.
Residential fibers typically include recycled newspapers. Newspapers contain a preponderance of coarse, high yield fibers, typically stone groundwood (SGW), thermomechanical pulp (TMP), and/or chemithermomechanical pulp (CTMP) fibers. Such coarse newsprint fibers are usually highly refined to cause fractures and fibrillations which aid in imparting strength to the resulting newsprint. Such refining changes the freeness of the coarse fiber from "high" freeness fibers to "low" freeness fibers. If such refined, high-yield, coarse, mechanically pulped fibers were used in a tissue making process the resulting sheet is not soft, and therefore much less desirable as a tissue product.
Another disadvantage of using recycled newspapers or other recycled fibers is that, typically, absorbency is lost after recycling fibers due to drying of the fibers. Consequently, these recycled fibers may not be suitable for use in tissue products.
A recent thorough discussion of the relationship between tissue softness and fiber coarseness is contained in Canadian Patent No. 2,076,615. Attempts to produce soft tissue or towel type sanitary paper products from a majority of high yield fibers such as CTMP, TMP or SGW pulp have not been successful. Likewise, producing soft tissue and towel products by recycling old newspapers has not been very successful partially because the predominant fiber in newsprint or in old newspapers are low freeness, coarse, high yield fibers.
Other complicating factors in producing soft tissue and towel products from recycled newspapers are problems with papermachine operation due to poor drainage of low freeness fibers and problems with fines and other substances that accumulate in the papermachine water system (whitewater). These materials make it difficult to crepe the tissue sheet from the Yankee drying cylinder, and therefore necessitate operating the papermachine at conditions which do not promote maximum softness.
Conventional recycling of newspapers/newsprint to obtain fibers comparable to the type of fibers used to originally make the newsprint is known in the art as "deinking" and typically involves pulping, washing, screening, centrifugal cleaning, solubilizing insoluble contaminants (usually by strong caustic treatments), washing and bleaching of the fibers to counteract the yellowing effects of caustic treatments.
The first step in conventional recycling of old newspapers is to separate the paper into individual fibers in water to form a pulp slurry. Caustic is added to facilitate the solubilization and separation of contaminants from the fibers. This is followed by removing inks and contaminants from the fibers by a combination of various process steps such as screening, centrifugal cleaning, washing, flotation and the like. The screening and centrifugal cleaning steps remove large contaminants such as paper clips, staples, plastics, etc. The primary purpose of washing and flotation steps is to suspend contaminants, such ash and inks, in the water and to remove the contaminants from the fibers.
When caustic is used to facilitate contaminant removal, some yellowing of the fibers unfortunately occurs due to the caustic treatment. After or during caustic treatment and washing, the fibers are usually bleached to counteract the yellowing effect of caustic or to produce better fibers having higher brightness than the fibers in the original waste paper. Cleaned, decontaminated, and bleached fibers are usually blended with virgin fibers and then used in a papermaking process for which the fibers properties are suitable. Because the starting fibers are newsprint type fibers (i.e., coarse, low freeness and low brightness fibers) such recycled fibers are most often reused for making blank newsprint. Their high coarseness and low freeness render them unsuitable for making soft tissue products unless blended with a majority of higher quality fibers such as bleached northern softwood kraft pulp. Unfortunately, these higher quality fibers tend to be more expensive, thereby raising the cost of the final product.
Conventional pulping of used newspaper to obtain recycled newsprint fiber is typically done in a high attrition pulper at a consistency of 4-18% and at 90.degree. F.-160.degree. F. for 20 minutes to 60 minutes, depending on the exact type of waste paper being processed. Caustic soda or other alkaline substances such as sodium silicate are commonly used to raise the pH of the pulp slurry to pH 9-10 to aid in separating fibers (defibering) and also to loosen the inks and separate dirt from the fiber. At an alkaline pH vegetable oils in the inks are saponified while mineral oils are emulsified by the combination of alkaline pH and soap, all of which enhance the removal of oils during washing. A surfactant deinking aid (for higher pH ranges) is usually added to further help separate inks from fiber.
The caustic step in recycling processes of old newsprint to obtain well cleaned quality fibers causes swelling of the fibers, and usually solubilizes many components. In addition to saponifying vegetable based printing oils, caustic also saponifies natural organic acids typically present in old newspapers to produce the corresponding soaps of the saponifiable materials. The saponified vegetable oils and organic acids so formed aid in removal of other contaminants from the fibers, such as non-saponifiable printing oils (mineral oil). These substances are subsequently removed from the fibers by washing and/or flotation after the caustic treatment.
A major recycler of old newspapers, Garden State Paper, in recent journal articles, one entitled "The Big `D`: Getting Rid of the Ink in Recycled Fiber," appearing in the journal Paper Age, 1991 Recycling Annual, at pages 23 and 50 and the other article entitled "Recycling From the Newsprint Perspective," at pages 9, 12 and 13 of the same 1991 Recycling Annual, (Paper Age, 1991 Recycling Annual) describes its newsprint recycling and deinking processes cleaning and screening followed by a series of 3 washings facilitated by the addition of chemicals to emulsify the printing oils and resins. Again the aim of this process is to remove printing ink constituents, including oils, as completely as possible. This is especially important because the recycled newsprint fiber is made into blank newsprint paper which would not have adequate brightness or strength without removing the ink constituents.
There is a long felt and unmet need for a soft paper product made from high-yield, coarse, fibers. There is also a need for an economical and practical process of treating high-yield, coarse fibers so they are suitable for making soft paper products. This need also extends to a process for treating newspapers/newsprint fibers so they are suitable for making soft paper products as well as soft paper products containing such treated fibers. Furthermore, there is a need to make high absorbency products from recycled coarse fibers.
Definitions
As used herein, the term "nonwoven web" refers to a web that has a structure of individual fibers or filaments which are interlaid forming a matrix, but not in an identifiable repeating manner. Nonwoven webs have been, in the past, formed by a variety of processes known to those skilled in the art such as, for example, meltblowing, spunbonding, wet-forming and various bonded carded web processes.
As used herein, the term "spunbonded web" refers to a web of small diameter fibers and/or filaments which are formed by extruding a molten thermoplastic material as filaments from a plurality of fine, usually circular, capillaries in a spinnerette with the diameter of the extruded filaments then being rapidly reduced, for example, by non-eductive or eductive fluid-drawing or other well known spunbonding mechanisms. The production of spunbonded nonwoven webs is illustrated in patents such as Appel, et al., U.S. Pat. No. 4,340,563.
As used herein, the term "meltblown fibers" means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into a high-velocity gas (e.g. air) stream which attenuates the filaments of molten thermoplastic material to reduce their diameters, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high-velocity gas stream and are deposited on a collecting surface to form a web of randomly disbursed meltblown fibers. The meltblown process is well-known and is described in various patents and publications, including NRL Report 4364, "Manufacture of Super-Fine Organic Fibers" by V. A. Wendt, E. L. Boone, and C. D. Fluharty; NRL Report 5265, "An Improved Device for the Formation of Super-Fine Thermoplastic Fibers" by K. D. Lawrence, R. T. Lukas, and J. A. Young; and U.S. Pat. No. 3,849,241, issued Nov. 19, 1974, to Buntin, et al.
As used herein, the term "microfibers" means small diameter fibers having an average diameter not greater than about 100 microns, for example, having a diameter of from about 0.5 microns to about 50 microns, more specifically microfibers may also have an average diameter of from about 1 micron to about 20 microns. Microfibers having an average diameter of about 3 microns or less are commonly referred to as ultra-fine microfibers. A description of an exemplary process of making ultra-fine microfibers may be found in, for example, U.S. Pat. No. 5,213,881, entitled "A Nonwoven Web With Improved Barrier Properties".
As used herein, the term "fibrous cellulosic material" refers to a nonwoven web including cellulosic fibers (e.g., pulp) that has a structure of individual fibers which are interlaid, but not in an identifiable repeating manner. Such webs have been, in the past, formed by a variety of nonwoven manufacturing processes known to those skilled in the art such as, for example, air-forming, wet-forming and/or paper-making processes. Exemplary fibrous cellulosic materials include papers, tissues and the like. Such materials can be treated to impart desired properties utilizing processes such as, for example, calendering, creping, hydraulic needling, hydraulic entangling and the like. Generally speaking, the fibrous cellulosic material may be prepared from cellulose fibers from synthetic sources or sources such as woody and non-woody plants. Woody plants include, for example, deciduous and coniferous trees. Non-woody plants include, for example, cotton, flax, esparto grass, milkweed, straw, jute, hemp, and bagasse. The cellulose fibers may be modified by various treatments such as, for example, thermal, chemical and/or mechanical treatments. It is contemplated that reconstituted and/or synthetic cellulose fibers may be used and/or blended with other cellulose fibers of the fibrous cellulosic material. Fibrous cellulosic materials may also be composite materials containing cellulosic fibers and one or more non-cellulosic fibers and/or filaments. A description of a fibrous cellulosic composite material may be found in, for example, U.S. Pat. No. 5,284,703.
As used herein, the term "pulp" refers to cellulosic fibrous material from sources such as woody and non-woody plants. Woody plants include, for example, deciduous and coniferous trees. Non-woody plants include, for example, cotton, flax, esparto grass, milkweed, straw, jute, hemp, and bagasse. Pulp may be modified by various treatments such as, for example, thermal, chemical and/or mechanical treatments.
As used herein, the term "machine direction" is the direction of a material parallel to its forward direction during processing.
As used herein, the term "cross direction" is the direction of a material perpendicular to its machine direction.
As used herein, the term "cup crush" refers to a test used to determine the detectable softness, particularly the stiffness, of a material by using the peak load and energy units from a constant-rate-of-extension (hereinafter referred to as "CRE") testing machine.
As used herein, the term "load" refers to the force, in weight units, applied to a body. The weight units may be reported in gram-force, which is force of a mass under earth's gravity and is analogous to the English units of pound-force. The term gram-force may be hereinafter abbreviated as "g.sub.f ".
As used herein, the term "energy" refers to the force times distance required to accomplish work and may be reported in units of gram-force times millimeter, which may be hereinafter abbreviated as "g.sub.f mm".
As used herein, the term "machine direction tensile" (hereinafter may be referred to as "MDT") is the breaking force in the machine direction required to rupture a one or three inch width specimen and may be reported as gram-force.
As used herein, the term "cross direction tensile" (hereinafter may be referred to as "CDT") is the breaking force in the cross direction required to rupture a one or three inch specimen and may be reported as gram-force.
As used herein, the term "basis weight" (hereinafter may be referred to as "BW") is the mass per unit area of a specimen and may be reported as gram per meter squared, which may be hereinafter abbreviated as "g/m.sup.2 ".
As used herein, the term "normalized tensile strength" (hereinafter may be referred to as "NTS") is the measurement of the strength of a material, generally a fabric or nonwoven web, and may be reported as gram-force times meter squared divided by gram, which may be hereinafter abbreviated as g.sub.f m.sup.2 /g. The greater the NTS generally relates to a stronger specimen. The NTS is calculated by the formula: EQU NTS=(MDT*CDT).sup.0.5 /BW
As used herein, the term "Kawabata Bending" refers to a test used to evaluate the amount of resistance one would feel by handling a material. The results of this test may be expressed as bending rigidity and bending hysterisis.
As used herein, the term "bending rigidity" refers to the resistance of a material to being bent. The larger the value, the more resistant the material is to being bent. The rigidity value may be expressed in units of gram-force times centimeter squared divided by centimeter, which may be hereinafter abbreviated as "g.sub.f cm.sup.2 /cm".
As used herein, the term "bending hysteresis" refers to the inability of material to recover after being bent. The larger the hysterisis value, the less ability the material has to recover. The hysterisis value may be expressed in units of gram-force times centimeter divided by centimeter, which may be hereinafter abbreviated as "g.sub.f cm/cm".
As used herein, the term "wicking" refers to a test used to measure the rate that a material absorbs liquid by capillary action. The results of this test may be expressed as XY wicking, Z wicking, and total wicking.
As used herein, the term "XY wicking" refers to how fast a liquid will redistribute itself away from the liquid source to the balance of the sheet and may be expressed as grams of liquid per gram of material per second, which may be hereinafter abbreviated as "g/g/s".
As used herein, the term "Z wicking" refers to how fast a liquid enters a material and is absorbed vertically from the bottom to the top of the material. Z wicking may be expressed as grams of liquid per gram of material per second, which may be hereinafter abbreviated as "g/g/s".
As used herein, the term "total wicking" refers to the total amount of liquid absorbed during a given time period, and may be expressed as grams of liquid per grams of material, which may be hereinafter abbreviated as "g/g".
As used herein, the term "bleaching" refers to a process where bleach is added to fibers, resulting in the whitening and brightening of the fibers.
As used herein, the term "coarseness" is the weight per unit length of fiber, expressed as milligrams per 100 meters. Typically, a fiber is considered coarse having a value greater than about 12 milligrams per 100 meters.
As used herein, the term "creped" refers to a crinkling surface of a material, such as paper. An exemplary process for creating a creped surface includes placing a paper sheet on the surface of a Yankee machine for drying and then removing the sheet with a doctor blade.
As used herein, the term "uncreped" refers to a material not having a creped surface.
As used herein, the term "ream" refers to a unit of area and is defined as 2880 square feet of a material.
As used herein, the term "office paper" refers to printing paper or fiber discarded in a typical business setting. Typically, these papers include at least 80 percent of higher grade, white-colored, or bleached papers that may be recycled to create higher quality paper products, such as tissue paper. However, some lower grade papers, such as chip board and dark colored papers, as well as some contaminants, such as hot melt adhesives and staples, may also be present, but no more than 20 percent of the total mix.
As used herein, the term "mixed residential paper or fiber" refers to fiber recovered from residences, such as old newspapers, groundwood, and magazines. Typically, these fibers include at up to 75 percent old newspapers and groundwood, and up to 10 percent corrugated paper. Typically, these papers may be recycled to create lower quality paper products, such as paper boards used in commercial cereal boxes.